title: Ambivalent roles of carboxypeptidase B in the lytic susceptibility of fibrin.
abstract: BACKGROUND
  Removal of C-terminal lysine residues that are continuously exposed in lysing fibrin is an established anti-fibrinolytic mechanism dependent on the plasma carboxypeptidase TAFIa, which also removes arginines that are exposed at the time of fibrinogen clotting by thrombin.
  
  
  OBJECTIVE
  To evaluate the impact of alterations in fibrin structure mediated by constitutive carboxypeptidase activity on the function of fibrin as a template for tissue plasminogen activator-(tPA) induced plasminogen activation and its susceptibility to digestion by plasmin.
  
  
  RESULTS
  We used the stable carboxypeptidase B (CPB), which shows the same substrate specificity as TAFIa. If 1.5 - 6μM fibrinogen was clotted in the presence of 8U/mL CPB, a denser fibrin network was formed with thinner fibers (the median fiber diameter decreased from 138 - 144nm to 89 - 109nm as established with scanning electron microscopy). If clotting was initiated in the presence of 5 - 10μM arginine, a similar decrease in fiber diameter (82 -95nm) was measured. The fine structure of arginine-treated fibrin enhanced plasminogen activation by tPA, but slowed down lysis monitored using fluorescent tPA and confocal laser microscopy. However, if lysis was initiated with plasmin in CPB-treated fibrin, the rate of dissolution increased to a degree corresponding to doubling of the plasmin concentration.
  
  
  CONCLUSIONS
  The present data evidence that CPB activity generates fine-mesh fibrin which is more difficult to lyse by tPA, but conversely, CPB and plasmin together can stimulate fibrinolysis, possibly by enhancing plasmin diffusion.
authors.affiliation: Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.
authors.forename: András
authors.initials: A
authors.lastname: Kovács
authors.affiliation: Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Szabó
authors.affiliation: Biotherapeutics, Haemostasis Section, National Institute for Biological Standards and Control, South Mimms, Potters Bar, UK.
authors.forename: Colin
authors.initials: C
authors.lastname: Longstaff
authors.affiliation: IT Department, N.Y. Vaptsarov Naval Academy, Varna, Bulgaria.
authors.forename: Kiril
authors.initials: K
authors.lastname: Tenekedjiev
authors.affiliation: Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.
authors.forename: Raymund
authors.initials: R
authors.lastname: Machovich
authors.affiliation: Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary. Electronic address: Krasimir.Kolev@eok.sote.hu.
authors.forename: Krasimir
authors.initials: K
authors.lastname: Kolev
mesh_terms: D000818:Animals; D001120:Arginine / Q000737:chemistry / Q000378:metabolism; D043424:Carboxypeptidase B / Q000737:chemistry / Q000378:metabolism*; D005337:Fibrin / Q000737:chemistry / Q000378:metabolism*; D005341:Fibrinolysin / Q000378:metabolism; D005342:Fibrinolysis / Q000502:physiology; D006801:Humans; D007700:Kinetics; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013552:Swine; D010959:Tissue Plasminogen Activator / Q000378:metabolism
chemical_list: D005337:Fibrin; D001120:Arginine; D043424:Carboxypeptidase B; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin
keywords: CPB; CPN; Carboxypeptidase; Fibrin; Fibrinolysis; Plasmin; TAFI; carboxypeptidase B; carboxypeptidase N; tPA; thrombin activatable fibrinolysis inhibitor; tissue-type plasminogen activator